Gate spacer structure and method of forming same

ABSTRACT

A semiconductor device and a method of forming the same are provided. The method includes forming a sacrificial gate structure over an active region. A first spacer layer is formed along sidewalls and a top surface of the sacrificial gate structure. A first protection layer is formed over the first spacer layer. A second spacer layer is formed over the first protection layer. A third spacer layer is formed over the second spacer layer. The sacrificial gate structure is replaced with a replacement gate structure. The second spacer layer is removed to form an air gap between the first protection layer and the third spacer layer.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/245,442, filed on Jan. 11, 2019, which claims the benefit of U.S.Provisional Application No. 62/753,139, filed on Oct. 31, 2018, whichapplications are hereby incorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as, for example, personal computers, cell phones, digital cameras,and other electronic equipment. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductor layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. However, asthe minimum features sizes are reduced, additional problems arise thatshould be addressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a perspective view of a fin field-effect transistor (“FinFET”)device in accordance with some embodiments.

FIGS. 2A-5A are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 6A and 6B are cross-sectional views of an intermediate stage inthe manufacture of a FinFET device in accordance with some embodiments.

FIGS. 7A, 7B and 7C are cross-sectional views of an intermediate stagein the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 8A, 8B and 8C are cross-sectional views of an intermediate stagein the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 9A, 9B and 9C are cross-sectional views of an intermediate stagein the manufacture of a FinFET device in accordance with someembodiments.

FIG. 10 is a cross-sectional view of a plasma deposition/dopingapparatus in accordance with some embodiments.

FIGS. 11A, 11B and 11C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 12A, 12B and 12C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 13A, 13B and 13C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 14A, 14B and 14C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 15A, 15B and 15C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 16A, 16B and 16C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIG. 17C is a cross-sectional view of an intermediate stage in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 18A, 18B and 18C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 19A, 19B and 19C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 20A, 20B and 20C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 21A, 21B and 21C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 22A, 22B and 22C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 23A, 23B and 23C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 24A, 24B and 24C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 25A, 25B and 25C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 26A, 26B and 26C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 27A, 27B and 27C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 28A, 28B and 28C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 29A, 29B and 29C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 30A, 30B and 30C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 31A, 31B and 31C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 32A, 32B and 32C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 33A, 33B and 33C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 34A, 34B and 34C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIGS. 35A, 35B and 35C are cross-sectional views of an intermediatestage in the manufacture of a FinFET device in accordance with someembodiments.

FIG. 36 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

FIG. 37 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

FIG. 38 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

FIG. 39 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

FIG. 40 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments will be described with respect to a specific context,namely, a gate spacer structure of a semiconductor device and a methodof forming the same. Various embodiments presented herein are discussedin the context of a FinFET device formed using a gate-last process. Inother embodiments, a gate-first process may be used. Also, someembodiments contemplate aspects used in planar transistor devices,multiple-gate transistor devices, 2D transistor devices, gate-all-aroundtransistor devices, nanowire transistor devices, or the like. Variousembodiments discussed herein allow for forming a gate spacer structurecomprising an air gap or an air spacer. In some embodiments, one or moreprotection layers are formed to protect spacer layers while enhancing anetch selectivity of a sacrificial layer to be removed to form an airspacer. In some embodiments, a protection layer is formed by depositingcarbon or boron on a spacer layer. In other embodiments, a protectionlayer is formed by doping a spacer layer with carbon or boron. In someembodiments, a protection layer is formed using a plasma-assisteddeposition/doping apparatus. Various embodiments discussed hereinfurther allow for improving structural integrity of gate spacerstructures during an etch process for forming an air spacer and reducingor avoiding a gate collapse.

FIG. 1 illustrates an example of a fin field-effect transistor (FinFET)100 in a three-dimensional view. The FinFET 100 comprises a fin 105 on asubstrate 101. The substrate 101 includes isolation regions 103, and thefin 105 protrudes above and from between neighboring isolation regions103. A gate dielectric 107 is along sidewalls and over a top surface ofthe fin 105, and a gate electrode 109 is over the gate dielectric 107.Source/drain regions 111 and 113 are disposed in opposite sides of thefin 105 with respect to the gate dielectric 107 and gate electrode 109.The FinFET 100 illustrated in FIG. 1 is provided for illustrativepurposes only and is not meant to limit the scope of the presentdisclosure. As such, many variations are possible, such as epitaxialsource/drain regions, multiple fins, multilayer fins, etc. FIG. 1further illustrates reference cross-sections that are used in subsequentfigures. Cross-section A-A is across a channel, the gate dielectric 107,and the gate electrode 109 of the FinFET 100. Cross-section C-C is in aplane that is parallel to the cross section A-A and is across fin 105outside of the channel. Cross-section B-B is perpendicular to thecross-sections A-A and C-C, and is along a longitudinal axis of the fin105 and in a direction of, for example, a current flow between thesource/drain regions 111 and 113. Subsequent figures refer to thesereference cross-sections for clarity.

FIGS. 2A-9A, 11A-16A, 18A-26A, 6B-9B, 11B-16B, 18B-26B, 7C-9C, and11C-26C are cross-sectional views of intermediate stages in themanufacturing of a FinFET device 200 in accordance with someembodiments. In FIGS. 2A-9A, 11A-16A, 18A-26A, 6B-9B, 11B-16B, 18B-26B,7C-9C, and 11C-26C, figures ending with an “A” designation areillustrated along the reference cross-section A-A illustrated in FIG. 1,except for multiple FinFETs and multiple fins per FinFET; figures endingwith a “B” designation are illustrated along the reference cross-sectionB-B illustrated in FIG. 1; and figures ending with a “C” designation areillustrated along the cross-section C-C illustrated in FIG. 1.

Referring to FIG. 2A, in some embodiments, the process of forming theFinFET device 200 starts with forming a mask 203 over a substrate 201.The substrate 201 may be a semiconductor substrate, such as a bulksemiconductor, a semiconductor-on-insulator (SOI) substrate, or thelike, which may be doped (e.g., with a p-type or an n-type dopant) orundoped. The substrate 201 may be a wafer, such as a silicon wafer.Generally, an SOI substrate comprises a layer of a semiconductormaterial formed on an insulator layer. The insulator layer may be, forexample, a buried oxide (BOX) layer, a silicon oxide layer, or the like.The insulator layer is provided on a substrate, typically a silicon orglass substrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the substrate 201 may include silicon; germanium; a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs,GaInP, and/or GaInAsP; or combinations thereof.

The substrate 201 may further include integrated circuit devices (notshown). As one of ordinary skill in the art will recognize, a widevariety of integrated circuit devices such as transistors, diodes,capacitors, resistors, the like, or combinations thereof may be formedin and/or on the substrate 201 to generate the structural and functionalrequirements of the design for the FinFET device 200. The integratedcircuit devices may be formed using any suitable methods.

In some embodiments, appropriate wells (not shown) may be formed in thesubstrate 201. In some embodiments where the resulting FinFET device 200is an n-type device, the wells are p-wells. In some embodiments wherethe resulting FinFET device 200 is a p-type device, the wells aren-wells. In other embodiments, both p-wells and n-wells are formed inthe substrate 201. In some embodiments, p-type impurities are implantedinto the substrate 201 to form the p-wells. The p-type impurities may beboron, BF₂, or the like. In some embodiments, n-type impurities areimplanted into the substrate 201 to form the n-wells. The n-typeimpurities may be phosphorus, arsenic, or the like. After implanting theappropriate impurities, an annealing process may be performed on thesubstrate 201 to activate the p-type and n-type impurities that wereimplanted.

FIG. 2A further illustrates the formation of a mask 203 over thesubstrate 201. In some embodiments, the mask 203 may be used in asubsequent etch step to pattern the substrate 201 (see FIG. 3A). In someembodiments, the mask 203 may comprise one or more mask layers. As shownin FIG. 2A, in some embodiments, the mask 203 may include a first masklayer 203A and a second mask layer 203B over the first mask layer 203A.The first mask layer 203A may be a hard mask layer, may comprise one ormore layers of silicon oxide, silicon nitride, silicon oxynitride,silicon carbide, silicon carbonitride, a combination thereof, or thelike, and may be formed using any suitable process, such as thermaloxidation, thermal nitridation, atomic layer deposition (ALD), physicalvapor deposition (PVD), chemical vapor deposition (CVD), a combinationthereof, or the like. The first mask layer 203A may be used to preventor minimize etching of the substrate 201 underlying the first mask layer203A in the subsequent etch step (see FIG. 3A). The second mask layer203B may comprise a photoresist, and in some embodiments, may be used topattern the first mask layer 203A for use in the subsequent etch step.The second mask layer 203B may be formed using a spin-on technique andmay be patterned using acceptable photolithography techniques. In someembodiments, the mask 203 may comprise three or more mask layers.

FIG. 3A illustrates the formation of semiconductor strips 301 in thesubstrate 201. First, mask layers 203A and 203B may be patterned, whereopenings in mask layers 203A and 203B expose areas of the substrate 201where trenches 303 are to be formed. Next, an etch process is performed,where the etch process creates the trenches 303 in the substrate 201through the openings in the mask 203. The remaining portions of thesubstrate 201 underlying the patterned mask 203 form a plurality ofsemiconductor strips 301. The etch process may comprise any acceptableetch process, such as a reactive ion etch (RIE), neutral beam etch(NBE), a combination thereof, or the like. The etch process may beanisotropic. In some embodiments, after forming the semiconductor strips301, any remaining portions of the mask 203 may be removed by anysuitable process. In other embodiments, portions of the mask 203, suchas the first mask layer 203A, may remain over the semiconductor strips301. In some embodiments, the semiconductor strips 301 may have a heightH₁ between about 50 nm and about 80 nm. In some embodiments, thesemiconductor strips 301 may have a width W₁ between about 5 nm andabout 10 nm.

FIG. 4A illustrates the formation of an insulation material in thetrenches 303 (see FIG. 3A) between neighboring semiconductor strips 301to form isolation regions 401. The insulation material may be an oxide,such as silicon oxide, a nitride, such as silicon nitride, a combinationthereof, or the like, and may be formed by a high density plasmachemical vapor deposition (HDP-CVD), a flowable CVD (FCVD) (e.g., aCVD-based material deposition in a remote plasma system and post curingto make it convert to another material, such as an oxide), a combinationthereof, or the like. Other insulation materials formed by anyacceptable processes may be also used.

Furthermore, in some embodiments, the isolation regions 401 may includea conformal liner (not illustrated) formed on sidewalls and bottomsurfaces of the trenches 303 (see FIG. 3A) prior to filling the trenches303 with the insulation material of the isolation regions 401. In someembodiments, the liner may comprise a semiconductor (e.g., silicon)nitride, a semiconductor (e.g., silicon) oxide, a thermal semiconductor(e.g., silicon) oxide, a semiconductor (e.g., silicon) oxynitride, apolymer, combinations thereof, or the like. The formation of the linermay include any suitable method, such as ALD, CVD, HDP-CVD, acombination thereof, or the like. In such embodiments, the liner mayprevent (or at least reduce) the diffusion of the semiconductor materialfrom the semiconductor strips 301 (e.g., Si or Ge) into the surroundingisolation regions 401 during the subsequent annealing of the isolationregions 401. In some embodiments, after the insulation material of theisolation regions 401 is deposited, an annealing process may beperformed on the insulation material of the isolation regions 401.

Referring further to FIG. 4A, a planarization process, such as achemical mechanical polishing (CMP) process, may remove any excessinsulation material of the isolation regions 401, such that top surfacesof the isolation regions 401 and top surfaces of the semiconductorstrips 301 are coplanar. In some embodiments where portions of the mask203 (see FIG. 3A) remain over the semiconductor strips 301 after formingthe semiconductor strips 301, the planarization process may also removethe remaining portions of the mask 203.

FIG. 5A illustrates the recessing of the isolation regions 401 to formshallow trench isolation (STI) regions 401. The isolation regions 401are recessed such that fins 501 protrude from between neighboringisolation regions 401. Further, the top surfaces of the isolationregions 401 may have a flat surface as illustrated, a convex surface, aconcave surface (such as dishing), or a combination thereof. The topsurfaces of the isolation regions 401 may be formed flat, convex, and/orconcave by an appropriate etch. The isolation regions 401 may berecessed using an acceptable etch process, such as one that is selectiveto the material of the isolation regions 401. In some embodiments, achemical oxide removal using a CERTAS® etch, an Applied Materials SICONItool, or dilute hydrofluoric (dHF) acid may be used.

A person having ordinary skill in the art will readily understand thatthe process described with respect to FIGS. 2A through 5A is just oneexample of how the fins 501 may be formed. In other embodiments, adielectric layer can be formed over a top surface of the substrate 201;trenches can be etched through the dielectric layer; homoepitaxialstructures can be epitaxially grown in the trenches; and the dielectriclayer can be recessed such that the homoepitaxial structures protrudefrom the dielectric layer to form fins. In yet other embodiments,heteroepitaxial structures can be used for the fins. For example, thesemiconductor strips 301 in FIG. 4A can be recessed, and one or morematerials different from the semiconductor strips 301 may be epitaxiallygrown in their place. In even further embodiments, a dielectric layercan be formed over a top surface of the substrate 201; trenches can beetched through the dielectric layer; heteroepitaxial structures can beepitaxially grown in the trenches using one or more materials differentfrom the substrate 201; and the dielectric layer can be recessed suchthat the heteroepitaxial structures protrude from the dielectric layerto form fins 501.

In some embodiments where homoepitaxial or heteroepitaxial structuresare epitaxially grown, the grown materials may be in situ doped duringgrowth. In other embodiments, homoepitaxial or heteroepitaxialstructures may be doped using, for example, ion implantation afterhomoepitaxial or heteroepitaxial structures are epitaxially grown. Invarious embodiments, the fins 501 may comprise silicon germanium(Si_(x)Ge_(1-x), where x can be between approximately 0 and 1), siliconcarbide, pure or substantially pure germanium, a III-V compoundsemiconductor, a II-VI compound semiconductor, or the like. For example,the available materials for forming III-V compound semiconductorinclude, but are not limited to, InAs, AlAs, GaAs, InP, GaN, InGaAs,InAlAs, GaSb, AlSb, AlP, GaP, and the like.

Referring to FIGS. 6A and 6B, a dielectric layer 601 is formed onsidewalls and top surfaces of the fins 501. In some embodiments, thedielectric layer 601 may be also formed over the isolation regions 401.In other embodiments, top surfaces of the isolation regions 401 may befree from the dielectric layer 601. The dielectric layer 601 maycomprise an oxide, such as silicon oxide, or the like, and may bedeposited (using, for example, ALD, CVD, PVD, a combination thereof, orthe like) or thermally grown (for example, using thermal oxidation, orthe like) according to acceptable techniques. In some embodiments, thedielectric layer 601 may comprise a dielectric material that has anacceptable breakdown voltage and leakage performance. A gate electrodelayer 603 is formed over the dielectric layer 601, and a mask 605 isformed over the gate electrode layer 603. In some embodiments, the gateelectrode layer 603 is deposited over the dielectric layer 601 and thenplanarized using, for example, a CMP process. The mask 605 is thendeposited over the gate electrode layer 603. The gate electrode layer603 may be made of, for example, polysilicon, although other materialsthat have a high etching selectivity with respect to the material of theisolation regions 401 may also be used. In other embodiments, the gateelectrode layer 603 may comprise one or more suitable metallicmaterials. The mask 605 may include one or more layers of, for example,silicon oxide, silicon nitride, silicon oxynitride, silicon carbide,silicon carbonitride, a combination thereof, or the like, and may beformed using any suitable process, such as thermal oxidation, thermalnitridation, ALD, PVD, CVD, a combination thereof, or the like.

Referring to FIGS. 7A, 7B, and 7C, the mask 605 (see FIGS. 6A and 6B)may be patterned using acceptable photolithography and etchingtechniques to form a patterned mask 701. The pattern of the patternedmask 701 is transferred to the gate electrode layer 603 and thedielectric layer 601 by acceptable etching techniques to form gates 703.The pattern of the gates 703 cover respective channel regions of thefins 501 (see FIG. 7B) while exposing source/drain regions of the fins501 (see FIG. 7C). The gates 703 may also have a lengthwise directionsubstantially perpendicular to the lengthwise direction of respectivefins 501 within process variations (see FIG. 7A). A size of the gates703, and a pitch between the gates 703, may depend on a region of a diein which the gates 703 are formed. In some embodiments, the gates 703may have a larger size and a larger pitch when located in, for example,an input/output region of a die (e.g., where input/output circuitry isdisposed) than when located in, for example, a logic region of a die(e.g., where logic circuitry is disposed). As described below in greaterdetail, the gates 703 are sacrificial gates and are subsequentlyreplaced by replacement gates. Accordingly, the gates 703 may also bereferred to as sacrificial gates or dummy gates. In other embodiments,the gates 703 are not replaced and remain in the final structure of theFinFET device 200.

Referring further to FIGS. 7A, 7B, and 7C, lightly doped source/drain(LDD) regions 705 may be formed in the substrate 201. Similar to theimplantation process discussed above with reference to FIG. 2A,appropriate impurities are implanted into the fins 501 to form the LDDregions 705. In some embodiments where the resulting FinFET device 200is a p-type device, p-type impurities are implanted into the fins 501 toform p-type LDD regions 705. In some embodiments where the resultingFinFET device 200 is an n-type device, n-type impurities are implantedinto the fins 501 to form n-type LDD regions 705. During theimplantation of the LDD regions 705, the gates 703 and the patternedmask 701 may act as a mask to prevent (or at least reduce) dopants fromimplanting into the channel regions of the fins 501. Thus, the LDDregions 705 may be formed substantially in the source/drain regions ofthe fins 501. The n-type impurities may be any of the n-type impuritiespreviously discussed, and the p-type impurities may be any of the p-typeimpurities previously discussed. After the implantation process, anannealing process may be performed to activate the implanted impurities.

Referring to FIGS. 8A, 8B, and 8C, a dielectric layer 801 is blanketformed on exposed surfaces of the gates 703, the patterned mask 701, theisolation regions 401, and the fins 501. In some embodiments, thedielectric layer 801 may comprise silicon nitride (SiN), siliconoxynitride (SiON), silicon oxycarbide (SiOC), silicon carbonitride(SiCN), silicon carboxynitride (SiOCN), a combination thereof, or thelike, and may be formed using CVD, ALD, a combination thereof, or thelike. The dielectric layer 801 may be also referred to as a spacerlayer. In some embodiments, the dielectric layer 801 has a thicknessbetween about 2 nm and about 4 nm.

Referring to FIGS. 9A, 9B, and 9C, a protection layer 901 is blanketformed over the dielectric layer 801. In some embodiments, theprotection layer 901 comprises carbon. In other embodiments, theprotection layer 901 comprises boron. In yet other embodiments, theprotection layer 901 is a carbon layer or a boron layer. In someembodiments, the protection layer 901 has a thickness between about 0.5nm and about 4 nm. As described below in greater detail, the protectionlayer 901 protects the dielectric layer 801 in a subsequent etch processfor forming an air gap (see FIGS. 24A, 24B, and 24C). In someembodiments, the protection layer 901 is formed using a plasma-assistedprocess, such as a plasma-enhanced CVD (PECVD), or the like. In someembodiments where the protection layer 901 comprises boron, theplasma-assisted process uses a gas mixture comprising a boron-containingprecursor gas. The boron-containing precursor gas may be B₂H₆, BF₃, acombination thereof, or the like. In some embodiments where theprotection layer 901 comprises carbon, the plasma-assisted process usesa gas mixture comprising a carbon-containing precursor gas. Thecarbon-containing precursor gas may be CH₄, CO, CO₂, a combinationthereof, or the like. In some embodiments, the gas mixture of theplasma-assisted process may also comprise an inert gas. The inert gasmay comprise xenon, helium, argon, neon, krypton, radon, the like, orcombinations thereof. As described below in greater detail, in someembodiments, the protection layer 901 may be formed using aplasma-assisted deposition/doping apparatus 1000 (see FIG. 10).

FIG. 10 is a cross-sectional view of a plasma-assisted deposition/dopingapparatus 1000 in accordance with some embodiments. The plasma-assisteddeposition/doping apparatus 1000 may be used to perform a depositionprocess for forming the protection layer 901 over the dielectric layer801 (see FIGS. 9A, 9B, and 9C). As described below in greater detail,the plasma-assisted deposition/doping apparatus 1000 may be also used toperform a doping process for doping the protection layer 901 to form aprotection layer (see FIGS. 28A, 28B, and 28C). The plasma-assisteddeposition/doping apparatus 1000 includes a chamber 1001 defined by ahousing 1003. A chuck 1005 in the chamber 1001 holds a wafer, such as awafer including the substrate 201. A gas inlet 1007 provides suitableprocess gasses to the chamber 1001. A plasma generator 1009 generatesplasma 1011 from the process gases. The plasma generator 1009 is coupledto a radio-frequency (RF) power source 1013 through a matching circuitsystem 1015. In some embodiments, the plasma generator 1009 may be atransformer-coupled plasma generator, inductively coupled plasma system,magnetically enhanced reactive ion etch system, electron cyclotronresonance system, a remote plasma generator, or the like. In someembodiment, the RF power source 1013 is operated at a power betweenabout 200 W and about 3300 W. A voltage source 1008 is coupled to thechuck 1005 to generate a bias voltage between the plasma generator 1009and the chuck 1005. In some embodiments, the voltage source 1008generates a pulsed DC bias voltage comprising DC voltage pulses(applying a negative DC bias voltage between the plasma generator 1009and the chuck 1005) separated by discharge steps (applying zero biasvoltage between the plasma generator 1009 and the chuck 1005). Each DCvoltage pulse may be from about −0.2 kV to about −10 kV. Each DC voltagepulse may have duration from about 20 μs to about 100 μs. The DC voltagepulses have a frequency from about 0.2 kHz to about 9 kHz.

In some embodiments, the plasma-assisted deposition/doping apparatus1000 may perform deposition and doping processes in an alternatingmanner. The deposition process is performed during discharge steps whenions of the plasma 1011 are neutralized at a surface of the wafer andare deposited over the dielectric layer 801 to form the protection layer901 (see FIGS. 9A, 9B, and 9C). The doping process is performed duringthe DC voltage pulse steps when ions of the plasma 1011 are acceleratedby the DC bias voltage of the DC voltage pulse and are implanted intothe dielectric layer 801 (see FIGS. 28A, 28B, and 28C).

Referring further to FIG. 10, in some embodiments, the plasma-assisteddeposition/doping apparatus 1000 may be configured to perform mainly adeposition process on the dielectric layer 801 without significantlydoping the dielectric layer 801. In such embodiments, the DC biasvoltage of the DC voltage pulses, the duration of the DC voltage pulsesand the frequency of the DC voltage pulses may be altered. For example,the DC bias voltage of the DC voltage pulses may be altered such thatenergy of ions of the plasma 1011 is insufficient to implant the ions ofthe plasma 1011 into the dielectric layer 801. Instead, the ions of theplasma 1011 are deposited over the dielectric layer 801. In someembodiments where the plasma-assisted deposition/doping apparatus 1000is configured to perform a deposition process, the DC bias voltage ofthe DC voltage pulses is from about 0.3 kV to about 5 kV. In someembodiments where the plasma-assisted deposition/doping apparatus 1000is configured to perform a deposition process, the duration of the DCvoltage pulses is from about 10 μs to about 100 μs. In some embodimentswhere the plasma-assisted deposition/doping apparatus 1000 is configuredto perform a deposition process, the frequency of the DC voltage pulsesis from about 500 Hz to about 9000 Hz.

In other embodiments, the plasma-assisted deposition/doping apparatus1000 may be configured to perform mainly a doping process on thedielectric layer 801 (see FIGS. 28A, 28B, and 28C) without performing asignificant deposition process. In such embodiments, the DC bias voltageof the DC voltage pulses, the duration of the DC voltage pulses and thefrequency of the DC voltage pulses may be altered. For example, the DCbias voltage of the DC voltage pulses may be altered such that energy ofions of the plasma 1011 is sufficient to implant the ions of the plasma1011 into the dielectric layer 801. Furthermore, the duration ofdischarge steps may be also reduced. In some embodiments where theplasma-assisted deposition/doping apparatus 1000 is configured toperform a doping process, the DC bias voltage of the DC voltage pulsesis from about 0.3 kV to about 5 kV. In some embodiments where theplasma-assisted deposition/doping apparatus 1000 is configured toperform a doping process, the duration of the DC voltage pulses is fromabout 10 μs to about 100 μs. In some embodiments where the plasmadeposition/doping apparatus 1000 is configured to perform a dopingprocess, the frequency of the DC voltage pulses is from about 500 Hz toabout 9000 Hz. In some embodiments where the plasma-assisteddeposition/doping apparatus 1000 is configured to perform a dopingprocess, the duration of discharge steps is from about 10 μs to about100 μs.

Referring to FIGS. 11A, 11B, and 11C, after forming the protection layer901, a dielectric layer 1101 is formed over the protection layer 901. Insome embodiments, the dielectric layer 1101 may be formed using similarmaterials and methods as the dielectric layer 801 described above withreference to FIGS. 8A, 8B, and 8C, and the description is not repeatedherein. In some embodiments, the dielectric layer 1101 and thedielectric layer 801 comprise a same material. In other embodiments, thedielectric layer 1101 and the dielectric layer 801 comprise differentmaterials. As described below in greater detail, the dielectric layer1101 is removed to form an air gap (see FIGS. 24A, 24B, and 24C), whilethe protection layer 901 protects the dielectric layer 801. Thedielectric layer 1101 may be also referred to as a spacer layer, or asacrificial spacer layer. In some embodiments, the dielectric layer 1101has a thickness between about 2 nm and about 5 nm.

FIGS. 12A-16A, 12B-16B, and 12C-16C illustrate formation of epitaxialsource/drain regions 1501 in the fins 501 between adjacent gates 703.Referring to FIGS. 12A, 12B, and 12C, a dielectric layer 1201 is formedover the dielectric layer 1101. In some embodiments, the dielectriclayer 1201 may be formed using similar materials and methods as thedielectric layer 801 described above with reference to FIGS. 8A, 8B, and8C, and the description is not repeated herein. In some embodiments, thedielectric layer 1201 and the dielectric layer 1101 comprise differentmaterials. As described below in greater detail, the dielectric layer1201 is removed after forming the epitaxial source/drain regions 1501.Accordingly, the dielectric layer 1201 may also be referred to as adummy layer or a sacrificial layer. In some embodiments, the dielectriclayer 1201 has a thickness between about 2 nm and about 4 nm.

Referring to FIGS. 13A, 13B, and 13C, a patterned mask 1301 is formedover the substrate 201 to protect the gates 703 and expose source/drainregions of the fins 501. A mask layer is deposited and patterned to formthe patterned mask 1301. In some embodiments, the mask layer maycomprise a photoresist, or the like, and may be formed using a spin-onprocess, or the like. In some embodiments where the mask layer comprisesa photoresist, the mask layer is patterned using suitablephotolithography methods.

Referring to FIGS. 14A, 14B, and 14C, after forming the patterned mask1301, a patterning process is performed on the dielectric layers 801,1101 and 1201, the protection layer 901, and the fins 501 to formrecesses 1401 in the source/drain regions of the fins 501. In someembodiments, the patterning process may include one or more suitableetch processes, such as anisotropic dry etch processes, while using thepatterned mask 1301 as an etch mask. The suitable anisotropic etchprocesses may include a reactive ion etch (RIE), a neutral beam etch(NBE), a combination thereof, or the like. In some embodiments,unprotected portions of the dielectric layer 1201 may not be fullyremoved while forming the recesses 1401. In such embodiments, portionsof the dielectric layer 1201 remain along sidewalls of the gates 703 inaddition to portions of the dielectric layer 1201 over the gates 703that were protected by the patterned mask 1301 (see FIG. 13B). Afterforming the recesses 1401, the patterned mask 1301 is removed. In someembodiments where the patterned mask 1301 comprises a photoresist, thepatterned mask 1301 is removed by an ashing process followed by a wetclean process.

Referring to FIGS. 15A, 15B, and 15C, epitaxial source/drain regions1501 are formed in the recesses 1401 (see FIGS. 14A, 14B, and 14C). Insome embodiments, the epitaxial source/drain regions 1501 areepitaxially grown in the recesses 1401 using metal-organic CVD (MOCVD),molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), vapor phaseepitaxy (VPE), selective epitaxial growth (SEG), a combination thereof,or the like. In some embodiments where the FinFET device 200 is ann-type device and the fins 501 are formed of silicon, the epitaxialsource/drain regions 1501 may include silicon, SiC, SiCP, SiP, or thelike. In some embodiments where the FinFET device 200 is a p-type deviceand the fins 501 are formed of silicon, the epitaxial source/drainregions 1501 may include SiGe, SiGeB, Ge, GeSn, or the like. Theepitaxial source/drain regions 1501 may have surfaces raised fromrespective surfaces of the fins 501 and may have facets. In someembodiments, the epitaxial source/drain regions 1501 may extend past thefins 501 and into the semiconductor strips 301. In some embodiments, thematerial of the epitaxial source/drain regions 1501 may be implantedwith suitable dopants. In some embodiments, the implantation process issimilar to the process used for forming the LLD regions 705 as describedabove with reference to FIGS. 7A, 7B, and 7C, and the description is notrepeated herein. In other embodiments, the material of the epitaxialsource/drain regions 1501 may be in situ doped during growth.

Referring to FIGS. 16A, 16B, and 16C, after forming the epitaxialsource/drain regions 1501, the remaining portions of the dielectriclayer 1201 are removed. In some embodiments, the remaining portions ofthe dielectric layer 1201 may be removed using a suitable etch processthat is selective to the material of the dielectric layer 1201. In theillustrated embodiment, each of the epitaxial source/drain regions 1501are physically separated from other epitaxial source/drain regions 1501.In other embodiments, adjacent epitaxial source/drain regions 1501 maybe merged. Such an embodiment is depicted in FIG. 17C, where adjacentepitaxial source/drain regions 1501 are merged to form a commonepitaxial source/drain region 1501 for multiple fins 501.

Referring to FIGS. 18A, 18B, and 18C, a dielectric layer 1801 is formedover the gates 703 and the epitaxial source/drain regions 1501 and aninterlayer dielectric (ILD) 1803 is formed over the dielectric layer1801. In some embodiments, the dielectric layer 1801 may be formed usingsimilar materials and methods as the dielectric layer 801 describedabove with reference to FIGS. 8A, 8B, and 8C, and the description is notrepeated herein. In some embodiments, the dielectric layer 1801 has athickness between about 2 nm and about 5 nm. In some embodiments, thedielectric layer 1801 and the dielectric layer 1201 comprise differentmaterials. The dielectric layer 1801 may be also referred to as a spacerlayer. In some embodiments, the dielectric layer 1801 is used as a stoplayer while patterning the ILD 1803 to form openings for subsequentlyformed contact plugs. In some embodiments, the ILD 1803 is a flowablefilm formed by a flowable CVD. In some embodiments, the ILD 1803 isformed of a dielectric material such as silicon oxide, SiOC, ZrO₂, HfO₂,Phospho-Silicate Glass (PSG), Boro-Silicate Glass (BSG), Boron-DopedPhospho-Silicate Glass (BPSG), undoped Silicate Glass (USG), low-kdielectric materials, extremely low-k dielectric materials, high-kdielectric materials, a combination thereof, or the like, and may bedeposited by any suitable method, such as CVD, PECVD, a spin-on-glassprocess, a combination thereof, or the like.

Referring to FIGS. 19A, 19B, and 19C, the ILD 1803 is recessed such thattopmost surfaces of remaining portions of the ILD 1803 are below topmostsurfaces of the gates 703. In some embodiments, the ILD 1803 may berecessed using a suitable etch process that is selective to the materialof the ILD 1803.

Referring to FIGS. 20A, 20B, and 20C, a dielectric layer 2001 is formedover the gates 703 and the ILD 1803. In some embodiments, the dielectriclayer 2001 may be formed using similar materials and methods as thedielectric layer 801 described above with reference to FIGS. 8A, 8B, and8C, and the description is not repeated herein. The dielectric layer2001 may also be referred to as a cap layer.

Referring to FIGS. 21A, 21B, and 21C, a planarization process, such as aCMP process, may be performed to level a top surface of dielectric layer2001 with the top surfaces of the gates 703. The planarization processalso removes the patterned mask 701 (see FIGS. 20A, 20B, and 20C),portions of the protection layer 901 and portions of the dielectriclayers 801, 1101 and 1801 that extend above the top surfaces of thegates 703.

FIGS. 22A and 23A, 22B and 23B, and 22C and 23C illustrate a gatereplacement process for forming the gates 2307. Referring to FIGS. 22A,22B, and 22C, the gate electrode layers 603 of the gates 703 (see FIGS.21A, 21B, and 21C) are removed using one or more suitable etch processesto form recesses 2201. Each of the recesses 2201 exposes a channelregion of a respective fin 501. In the illustrated embodiment, thedielectric layers 601 remain over the channel regions of the fins 501.In other embodiments, the dielectric layers 601 may also be removedduring the formation of the recesses 2201.

Referring to FIGS. 23A, 23B, and 23C, a gate dielectric layer 2301, awork function layer 2303, and a gate electrode layer 2305 are formed inthe recesses 2201 (see FIG. 22B). In some embodiments, the gatedielectric layer 2301 is conformally deposited in the recesses 2201. Insome embodiments, the gate dielectric layer 2301 comprises siliconoxide, silicon nitride, or multilayers thereof. In other embodiments,the gate dielectric layer 2301 includes a high-k dielectric material,and in these embodiments, the gate dielectric layer 2301 may have a kvalue greater than about 7.0, and may include a metal oxide or asilicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, and combinations thereof.The formation methods of the gate dielectric layer 2301 may includeMolecular-Beam Deposition (MBD), ALD, PECVD, a combination thereof, orthe like.

In some embodiments where the dielectric layers 601 are not removed overthe channel regions of the fins 501 while forming the recesses 2201, thedielectric layers 601 may act as interfacial layers between the gatedielectric layer 2301 and the channel regions of the fins 501. In someembodiments where the dielectric layers 601 are removed over the channelregions of the fins 501 while forming the recesses 2201, one or moreinterfacial layers may be formed over the channel regions of the fins501 prior to forming the gate dielectric layer 2301, and the gatedielectric layer 2301 is formed over the one or more interfacial layers.The interfacial layers help to buffer the subsequently formed high-kdielectric layer from the underlying semiconductor material. In someembodiments, the interfacial layers comprise a chemical silicon oxide,which may be formed of chemical reactions. For example, a chemical oxidemay be formed using deionized water+ozone (O₃), NH₄OH+H₂O₂+H₂O (APM), orother methods. Other embodiments may utilize a different material orprocesses (e.g., a thermal oxidation or a deposition process) forforming the interfacial layers.

After forming the gate dielectric layer 2301, the work function layer2303 is formed over the gate dielectric layer 2301. In some embodimentswhere the FinFET device 200 is an n-type device, the work function layer2303 comprises Ti, Ag, Al, TiAl, TiAlN, TiAlC, TaC, TaCN, TaSiN, TaAlC,Mn, Zr, a combination thereof, or the like, and may be formed using ALD,CVD, PVD, combinations thereof, or the like. In some embodiments wherethe FinFET device 200 is a p-type device, the work function layer 2303comprises TiN, WN, TaN, Ru, Co, a combination thereof, or the like, andmay be formed using ALD, CVD, PVD, combinations thereof, or the like.After forming the work function layer 2303, remaining portions of therecesses 2201 (see FIG. 22B) are filled with a gate electrode layer2305. In some embodiments, the gate electrode layer 2305 comprises Co,Ru, Al, Ag, Au, W, Ni, Ti, Cu, Mn, Pd, Re, Ir, Pt, Zr, alloys thereof,combinations thereof, or the like, and may be formed using ALD, CVD,PVD, plating, combinations thereof, or the like. After filling therecesses 2201 with the gate electrode layer 2305, a planarizationprocess, such as a CMP process, may be performed to remove the excessportions of the gate dielectric layer 2301, the work function layer2303, and the gate electrode layer 2305, which excess portions are overthe top surface of the dielectric layer 2001. The portions of the gatedielectric layer 2301, the work function layer 2303, and the gateelectrode layer 2305 remaining in the recesses 2201 in combination withrespective dielectric layers 601 form the gates 2307 in the recesses2201. The gates 2307 may also be referred to as replacement gates.

Referring to FIGS. 24A, 24B, and 24C, after forming the gates 2307, theremaining portions of the dielectric layer 1101 (see FIGS. 24A, 24B, and24C) are removed to form gaps 2401. The gaps 2401 may also be referredto as air gaps of air spacers. In some embodiments, the remainingportions of the dielectric layer 1101 may be removed using a suitableetch process that is selective to the material of the dielectric layer1101. In some embodiments, the suitable etch process may be a wet etchprocess performed by a mixture of HF and H₂O. In other embodiments, thesuitable etch process may be a dry etch process performed by a plasmagenerated from a mixture of HF and NF₃. In some embodiments, theprotection layer 901 protects the dielectric layer 801 from the etchprocess and improves etch selectivity of the dielectric layer 1101during the etch process. Furthermore, the protection layer 901 improvesstructural integrity of gate spacer structures comprising the dielectriclayers 801 and 1801, the protection layer 901, and the gaps 2401 toreduce or avoid collapsing of the gates 2307. In the illustratedembodiment, the gaps 2401 are formed after performing the gatereplacement process for forming the gates 2307. In other embodiments,the gaps 2401 may be formed after performing the planarization processdescribed above with reference to FIGS. 21A, 21B, and 21C, and beforeperforming the gate replacement process for forming the gates 2307.

Referring to FIGS. 25A, 25B, and 25C, an ILD 2501 is formed over thegates 2307. In some embodiments, the ILD 2501 may be formed usingsimilar materials and methods as the ILD 1803 described above withreference to FIGS. 18A, 18B and 18C, and the description is not repeatedherein. In some embodiments, the ILD 2501 does not extend into the gaps2401. In other embodiments, portions 2501 a of the ILD 2501 extend intothe gaps 2401. In some embodiments, the ILD 2501 and the ILD 1803 areformed of a same material. In other embodiments, the ILD 2501 and theILD 1803 are formed of different materials. The dielectric layers 1801and 2001, and the ILDs 1803 and 2501 are patterned to form openings 2503and 2505. In some embodiments, the dielectric layers 1801 and 2001, andthe ILDs 1803 and 2501 may be patterned using acceptablephotolithography and etching techniques. The openings 2503 expose therespective gates 2307. The openings 2505 expose the respective epitaxialsource/drain regions 1501. As described below in greater detail, theopenings 2503 and 2505 are filled with one or more conductive materialsto form contact plugs that provide electrical connections to theepitaxial source/drain regions 1501 and the gates 2307.

Referring further to FIGS. 25A, 25B, and 25C, self-aligned silicide(salicide) layers 2507 are formed through the openings 2503 and 2505. Insome embodiments, a metallic material is deposited in the openings 2503and 2505. The metallic material may comprise Ti, Co, Ni, NiCo, Pt, NiPt,Ir, PtIr, Er, Yb, Pd, Rh, Nb, a combination thereof, or the like, andmay be formed using PVD, sputtering, or the like. Subsequently, anannealing process is performed to form the salicide layers 2507. In someembodiments where the epitaxial source/drain regions 1501 comprisesilicon, the annealing process causes the metallic material to reactwith silicon to form a silicide of the metallic material.

Referring to FIGS. 26A, 26B, and 26C, the openings 2503 and 2505 (seeFIGS. 25A, 25B, and 25C) are filled with one or more conductivematerials to form contact plugs 2601 and 2603, respectively. In someembodiments, a liner (not shown), such as a diffusion barrier layer, anadhesion layer, or the like, and a conductive material are formed in theopenings 2503 and 2505. The liner may include titanium, titaniumnitride, tantalum, tantalum nitride, a combination thereof, or the like,and may be formed CVD, PVD, ALD, a combination thereof, or the like. Theconductive material may be copper, a copper alloy, silver, gold,tungsten, aluminum, nickel, a combination thereof, or the like, and maybe formed using CVD, PVD, ALD, an electrochemical plating process, anelectroless plating process, a combination thereof, or the like. Aplanarization process, such as a CMP process, may be performed to removeexcess portions of the liner and the conductive material from a topsurface of the ILD 2501. The remaining portions of the liner and theconductive material form contact plugs 2601 and 2603 in the openings2503 and 2505, respectively. The contact plugs 2601 are physically andelectrically coupled to the gates 2307. The contact plugs 2603 arephysically coupled to the salicide layers 2507. The contact plugs 2603are electrically coupled to the epitaxial source/drain regions 1501through the salicide layers 2507.

FIGS. 27A-29A, 27B-29B, and 27C-29C are cross-sectional views ofintermediate stages in the manufacturing of a FinFET device 2700 inaccordance with some embodiments. In FIGS. 27A-29A, 27B-29B, and27C-29C, figures ending with an “A” designation are illustrated alongthe reference cross-section A-A illustrated in FIG. 1, except formultiple FinFETs and multiple fins per FinFET; figures ending with a “B”designation are illustrated along the reference cross-section B-Billustrated in FIG. 1; and figures ending with a “C” designation areillustrated along the cross-section C-C illustrated in FIG. 1. In someembodiments, process steps for forming the FinFET device 2700 may besimilar to the process steps for forming the FinFET device 200 describedabove with reference to FIGS. 2A-9A, 11A-16A, 18A-26A, 6B-9B, 11B-16B,18B-26B, 7C-9C, and 11C-26C, with like features labeled by likenumerical references, and their description is not repeated herein.

In some embodiments, the process of forming the FinFET device 2700starts with forming a structure illustrated in FIGS. 7A, 7B, and 7C. Theprocess steps for forming the structure of FIGS. 7A, 7B, and 7C aredescribed above with reference to FIGS. 2A-7A, 6B, 7B, 7C, and thedescription is not repeated herein. Referring to FIGS. 27A, 27B, and27C, a dielectric layer 801 is blanket formed on exposed surfaces of thegates 703, the patterned mask 701, the isolation regions 401, and thefins 501. In some embodiments, the dielectric layer 801 is formed asdescribed above with reference to FIGS. 8A, 8B, and 8C, and thedescription is not repeated herein.

Referring to FIGS. 28A, 28B, and 28C, upper portion of the dielectriclayer 801 is doped to form a doped portion of the dielectric layer 801.The doped portion of the dielectric layer 801 forms a protection layer2801 over un-doped portion of the dielectric layer 801. In someembodiments, the upper portion of the dielectric layer 801 may be dopedusing carbon. In other embodiments, the upper portion of the dielectriclayer 801 may be doped using boron. In some embodiments, the dopingprocess is a plasma-assisted doping process performed by theplasma-assisted deposition/doping apparatus 1000 in a doping regime asdescribed above with reference to FIG. 10, and the description is notrepeated herein. In some embodiments where the upper portion of thedielectric layer 801 is doped with carbon, the plasma-assisted dopingprocess uses a gas mixture comprising a carbon-containing precursor gas.The carbon-containing precursor gas may be CH₄, or the like. In someembodiments, the implantation energy of carbon ions may be from about0.5 KeV to about 5 KeV. In some embodiments, a dosage of the implantedcarbon may be from about 5E13 atoms/cm² to about 1E15 atoms/cm². In someembodiments where the upper portion of the dielectric layer 801 is dopedwith boron, the plasma-assisted doping process uses a gas mixturecomprising a boron-containing precursor gas. The boron-containingprecursor gas may be B₂H₆, or the like. In some embodiments, theimplantation energy of boron ions may be from about 1 KeV to about 3KeV. In some embodiments, a dosage of the implanted boron may be fromabout 5E13 atoms/cm² to about 1E15 atoms/cm².

Referring further to FIGS. 28A, 28B, and 28C, by performing theplasma-assisted doping process, uniformity of dopants within theprotection layer 2801 is improved. The doping process alters etchcharacteristics of the doped portion of the dielectric layer 801. Insome embodiments, an etch rate of the protection layer 2801 is reducedcompared to an etch rate of the un-doped portion of the dielectric layer801. In some embodiments where the dielectric layer 801 comprises SiOCNand the carbon doping process is performed using the carbon-containingprecursor gas CH₄, with the implantation energy of about 2 KeV and thedosage of about 5E15 atoms/cm², the etch rate of the protection layer2801 is reduced by about 50% compared to the etch rate of the un-dopedportion of the dielectric layer 801 with respect to a wet etch processperformed using a mixture of HF and H₂O. In some embodiments where thedielectric layer 801 comprises SiN and the carbon doping process isperformed using the carbon-containing precursor gas CH₄, with theimplantation energy of about 2 KeV and the dosage of about 3E15atoms/cm², the etch rate of the protection layer 2801 is reduced byabout 70% compared to the etch rate of the un-doped portion of thedielectric layer 801 with respect to a wet etch process performed usinga mixture of HF and H₂O. In some embodiments where the dielectric layer801 comprises SiCN and the carbon doping process is performed using thecarbon-containing precursor gas CH₄, with the implantation energy fromabout 1.5 keV to about 2 KeV and the dosage of about 5E15 atoms/cm², theetch rate of the protection layer 2801 is reduced by more than about 95%compared to the etch rate of the un-doped portion of the dielectriclayer 801 with respect to a wet etch process performed using a mixtureof HF and H₂O. In some embodiments where the dielectric layer 801comprises SiOCN and the carbon doping process is performed using thecarbon-containing precursor gas CH₄, with the implantation energy ofabout 2 KeV and the dosage of about 5E15 atoms/cm², the etch rate of theprotection layer 2801 is reduced by about 50% compared to the etch rateof the un-doped portion of the dielectric layer 801 with respect to adry etch process performed using a plasma generated from a mixture of HFand NF₃. In some embodiments where the dielectric layer 801 comprisesSiCN and the carbon doping process is performed using thecarbon-containing precursor gas CH₄, with the implantation energy fromabout 0.3 keV to about 1 KeV and the dosage of about 4E15 atoms/cm², theetch rate of the protection layer 2801 is reduced by more than about 75%compared to the etch rate of the un-doped portion of the dielectriclayer 801 with respect to a dry etch process performed using a plasmagenerated from a mixture of HF and NF₃.

Referring to FIGS. 29A, 29B, and 29C, the process steps described abovewith reference to FIGS. 11A-16A, 18A-26A, 11B-16B, 18B-26B, and 11C-26Care performed on the structure of FIGS. 29A, 29B, and 29C to form theFinFET device 2700, and the description is not repeated herein. In someembodiments, the protection layer 2801 protects the un-doped portion ofthe dielectric layer 801 from the etch process that removes thedielectric layer 1101 and forms the gaps 2401, and improves etchselectivity of the dielectric layer 1101 during the etch process.Furthermore, the protection layer 2801 improves structural integrity ofgate spacer structures comprising the dielectric layers 801 and 1801,the protection layer 2801, and the gaps 2401 to reduce or avoidcollapsing of the gates 2307.

FIGS. 30A-33A, 30B-33B, and 30C-33C are cross-sectional views ofintermediate stages in the manufacturing of a FinFET device 3000 inaccordance with some embodiments. In FIGS. 30A-33A, 30B-33B, and30C-33C, figures ending with an “A” designation are illustrated alongthe reference cross-section A-A illustrated in FIG. 1, except formultiple FinFETs and multiple fins per FinFET; figures ending with a “B”designation are illustrated along the reference cross-section B-Billustrated in FIG. 1; and figures ending with a “C” designation areillustrated along the cross-section C-C illustrated in FIG. 1. In someembodiments, process steps for forming the FinFET device 3000 may besimilar to the process steps for forming the FinFET device 200 describedabove with reference to FIGS. 2A-9A, 11A-16A, 18A-26A, 6B-9B, 11B-16B,18B-26B, 7C-9C, and 11C-26C, with like features labeled by likenumerical references, and their description is not repeated herein.

In some embodiments, the process of forming the FinFET device 3000starts with forming a structure illustrated in FIGS. 8A, 8B, and 8C. Theprocess steps for forming the structure of FIGS. 8A, 8B, and 8C aredescribed above with reference to FIGS. 2A-8A, 6B-8B, and 7C-8C, and thedescription is not repeated herein. Referring to FIGS. 30A, 30B, and30C, a dielectric layer 1101 is formed over the dielectric layer 801. Insome embodiments, the dielectric layer 1101 is formed as described abovewith reference to FIGS. 11A, 11B, and 11C, and the description is notrepeated herein. Subsequently, a dielectric layer 1201 is formed overthe dielectric layer 1101. In some embodiments, the dielectric layer1201 is formed as described above with reference to FIGS. 12A, 12B, and12C, and the description is not repeated herein.

Referring to FIGS. 31A, 31B, and 31C, process steps described above withreference to FIGS. 13A-16A, 13B-16B, and 13C-16C are performed on thestructure of FIGS. 30A, 30B, and 30C to form epitaxial source/drainregions 1501, and the description is not repeated herein.

Referring to FIGS. 32A, 32B, and 32C, a protection layer 3201 is formedover the gates 703 and the epitaxial source/drain regions 1501. In someembodiments, the protection layer 3201 may be formed using similarmaterials and methods as the protection layer 901 described above withreference to FIGS. 9A, 9B and 9C, and the description is not repeatedherein.

Referring to FIGS. 33A, 33B, and 33C, the process steps described abovewith reference to FIGS. 18A-26A, 18B-26B, and 18C-26C are performed onthe structure of FIGS. 32A, 32B, and 32C to form the FinFET device 3000,and the description is not repeated herein. In some embodiments, theprotection layer 3201 protects the dielectric layer 1801 from the etchprocess that removes the dielectric layer 1101 and forms the gaps 2401,and improves etch selectivity of the dielectric layer 1101 during theetch process. Furthermore, the protection layer 3201 improves structuralintegrity of gate spacer structures comprising the dielectric layers 801and 1801, the protection layer 3201, and the gaps 2401 to reduce oravoid collapsing of the gates 2307.

FIGS. 34A, 34B, and 34C are cross-sectional views of a FinFET device3400 in accordance with some embodiments. In FIGS. 34A, 34B, and 34C,figures ending with an “A” designation are illustrated along thereference cross-section A-A illustrated in FIG. 1, except for multipleFinFETs and multiple fins per FinFET; figures ending with a “B”designation are illustrated along the reference cross-section B-Billustrated in FIG. 1; and figures ending with a “C” designation areillustrated along the cross-section C-C illustrated in FIG. 1. In someembodiments, process steps for forming the FinFET device 3400 may besimilar to the process steps for forming the FinFET device 200 describedabove with reference to FIGS. 2A-9A, 11A-16A, 18A-26A, 6B-9B, 11B-16B,18B-26B, 7C-9C, and 11C-26C, with like features labeled by likenumerical references, and their description is not repeated herein.

In some embodiments, the process of forming the FinFET device 3400starts with forming a structure illustrated in FIGS. 16A, 16B, and 16C.The process steps for forming the structure of FIGS. 16A, 16B, and 16Care described above with reference to FIGS. 2A-9A, 11A-16A, 6B-9B,11B-16B, 7C-9C, and 11C-16C, and the description is not repeated herein.Subsequently, the process steps described above with reference to FIGS.32A, 33A, 32B, 33B, 32C, and 33C are performed on the structure of FIGS.16A, 16B, and 16C to form the FinFET device 3400, and the description isnot repeated herein. In some embodiments, the protection layer 901protects the dielectric layer 801 and the protection layer 3201 protectsthe dielectric layer 1801 from the etch process that removes thedielectric layer 1101 and forms the gaps 2401. In addition, protectionlayers 901 and 3201 improve etch selectivity of the dielectric layer1101 during the etch process. Furthermore, the protection layers 901 and3201 improve structural integrity of gate spacer structures comprisingthe dielectric layers 801 and 1801, the protection layers 901 and 3201,and the gaps 2401 to reduce or avoid collapsing of the gates 2307. Insome embodiments, the protection layer 901 and the protection layer 3201comprise a same material. In some embodiments, the protection layer 901and the protection layer 3201 comprise different materials.

FIGS. 35A, 35B, and 35C are cross-sectional views of a FinFET device3500 in accordance with some embodiments. In FIGS. 35A, 35B, and 35C,figures ending with an “A” designation are illustrated along thereference cross-section A-A illustrated in FIG. 1, except for multipleFinFETs and multiple fins per FinFET; figures ending with a “B”designation are illustrated along the reference cross-section B-Billustrated in FIG. 1; and figures ending with a “C” designation areillustrated along the cross-section C-C illustrated in FIG. 1. In someembodiments, process steps for forming the FinFET device 3500 may besimilar to the process steps for forming the FinFET device 3400described above with reference to FIGS. 34A, 34B, and 34C, with likefeatures labeled by like numerical references, and their description isnot repeated herein.

In some embodiments, the process of forming the FinFET device 3500starts with forming a structure illustrated in FIGS. 28A, 28B, and 28C.The process steps for forming the structure of FIGS. 28A, 28B, and 28Care described above with reference to FIGS. 2A-7A, 27A, 28A, 6B, 7B,27B, 28B, 7C, 27C, and 28C, and the description is not repeated herein.Subsequently, the process steps described above with reference to FIGS.11A-16A, 11B-16B, and 11C-16C followed by the process steps describedabove with reference to FIGS. 32A, 33A, 32B, 33B, 32C, and 33C areperformed on the structure of FIGS. 28A, 28B, and 28C to form the FinFETdevice 3500, and the description is not repeated herein. In someembodiments, the protection layer 2801 protects the un-doped portion ofthe dielectric layer 801 and the protection layer 3201 protects thedielectric layer 1801 from the etch process that removes the dielectriclayer 1101 and forms the gaps 2401. In addition, protection layers 2801and 3201 improve etch selectivity of the dielectric layer 1101 duringthe etch process. Furthermore, the protection layers 2801 and 3201improve structural integrity of gate spacer structures comprising thedielectric layers 801 and 1801, the protection layers 2801 and 3201, andthe gaps 2401 to reduce or avoid collapsing of the gates 2307.

FIG. 36 is a flow diagram illustrating a method 3600 of forming asemiconductor device in accordance with some embodiments. The method3600 starts with step 3601, where a sacrificial gate (such as the gate703 illustrated in FIGS. 7A, 7B, and 7C) is formed over an active region(such as the fin 501 illustrated in FIGS. 7A, 7B, and 7C) as describedabove with reference to FIGS. 2A-7A, 6B, 7B, and 7C. In step 3603, afirst spacer layer (such as the dielectric layer 801 illustrated inFIGS. 8A, 8B, and 8C) is formed along sidewalls and a top surface of thesacrificial gate as described above with reference to FIGS. 8A, 8B, and8C. In step 3605, a protection layer (such as the protection layer 901illustrated in FIGS. 9A, 9B, and 9C) is formed over the first spacerlayer as described above with reference to FIGS. 9A, 9B, and 9C. In step3607, a second spacer layer (such as the dielectric layer 1101illustrated in FIGS. 11A, 11B, and 11C) is formed over the protectionlayer as described above with reference to FIGS. 11A, 11B, and 11C. Instep 3609, epitaxial source/drain regions (such as the epitaxialsource/drain regions 1501 illustrated in FIGS. 16A, 16B, and 16C) areformed in the active region as described above with reference to FIGS.12A-16A, 12B-16B, and 12C-16C. In step 3611, a third spacer layer (suchas the dielectric layer 1801 illustrated in FIGS. 18A, 18B, and 18C) isformed over the second spacer layer and the epitaxial source/drainregions as described above with reference to FIGS. 18A, 18B, and 18C. Instep 3613, the sacrificial gate is replaced with a replacement gate(such as the gate 2307 illustrated in FIGS. 23A, 23B, and 23C) asdescribed above with reference to FIGS. 19A-23A, 19B-23B, and 19C-23C.In step 3615, the second spacer layer is removed to form an air gap(such as the gap 2401 illustrated in FIGS. 24A, 24B, and 24C) betweenthe protection layer and the third spacer layer as described above withreference to FIGS. 24A, 24B, and 24C. In step 3617, contact plugs (suchas the contact plugs 2601 and 2603 illustrated in FIGS. 26A, 26B, and26C) are formed as described above with reference to FIGS. 25A, 26A,25B, 26B, 25C, and 26C.

FIG. 37 is a flow diagram illustrating a method 3700 of forming asemiconductor device in accordance with some embodiments. The method3700 starts with step 3701, where a sacrificial gate (such as the gate703 illustrated in FIGS. 27A, 27B, and 27C) is formed over an activeregion (such as the fin 501 illustrated in FIGS. 27A, 27B, and 27C) asdescribed above with reference to FIGS. 2A-7A, 6B, 7B, and 7C. In step3703, a first spacer layer (such as the dielectric layer 801 illustratedin FIGS. 27A, 27B, and 27C) is formed along sidewalls and a top surfaceof the sacrificial gate as described above with reference to FIGS. 27A,27B, and 27C. In step 3705, a portion of the first spacer layer is dopedto form a protection layer (such as the protection layer 2801illustrated in FIGS. 28A, 28B, and 28C) as described above withreference to FIGS. 28A, 28B, and 28C. In step 3707, a second spacerlayer (such as the dielectric layer 1101 illustrated in FIGS. 11A, 11B,and 11C) is formed over the protection layer as described above withreference to FIGS. 11A, 11B, and 11C. In step 3709, epitaxialsource/drain regions (such as the epitaxial source/drain regions 1501illustrated in FIGS. 29A, 29B, and 29C) are formed in the active regionas described above with reference to FIGS. 12A-16A, 12B-16B, and12C-16C. In step 3711, a third spacer layer (such as the dielectriclayer 1801 illustrated in FIGS. 29A, 29B, and 29C) is formed over thesecond spacer layer and the epitaxial source/drain regions as describedabove with reference to FIGS. 18A, 18B, and 18C. In step 3713, thesacrificial gate is replaced with a replacement gate (such as the gate2307 illustrated in FIGS. 29A, 29B, and 29C) as described above withreference to FIGS. 19A-23A, 19B-23B, and 19C-23C. In step 3715, thesecond spacer layer is removed to form an air gap (such as the gap 2401illustrated in FIGS. 29A, 29B, and 29C) between the protection layer andthe third spacer layer as described above with reference to FIGS. 24A,24B, and 24C. In step 3717, contact plugs (such as the contact plugs2601 and 2603 illustrated in FIGS. 29A, 29B, and 29C) are formed asdescribed above with reference to FIGS. 25A, 26A, 25B, 26B, 25C, and26C.

FIG. 38 is a flow diagram illustrating a method 3800 of forming asemiconductor device in accordance with some embodiments. The method3800 starts with step 3801, where a sacrificial gate (such as the gate703 illustrated in FIGS. 30A, 30B, and 30C) is formed over an activeregion (such as the fin 501 illustrated in FIGS. 30A, 30B, and 30C) asdescribed above with reference to FIGS. 2A-7A, 6B, 7B, and 7C. In step3803, a first spacer layer (such as the dielectric layer 801 illustratedin FIGS. 30A, 30B, and 30C) is formed along sidewalls and a top surfaceof the sacrificial gate as described above with reference to FIGS. 30A,30B, and 30C. In step 3805, a second spacer layer (such as thedielectric layer 1101 illustrated in FIGS. 30A, 30B, and 30C) is formedover the first spacer layer as described above with reference to FIGS.30A, 30B, and 30C. In step 3807, epitaxial source/drain regions (such asthe epitaxial source/drain regions 1501 illustrated in FIGS. 31A, 31B,and 31C) are formed in the active region as described above withreference to FIGS. 12A-16A, 12B-16B, and 12C-16C. In step 3809, aprotection layer (such as the protection layer 3201 illustrated in FIGS.32A, 32B, and 32C) is formed over the second spacer layer and theepitaxial source/drain regions as described above with reference toFIGS. 32A, 32B, and 32C. In step 3811, a third spacer layer (such as thedielectric layer 1801 illustrated in FIGS. 33A, 33B, and 33C) is formedover the protection layer as described above with reference to FIGS.18A, 18B, and 18C. In step 3813, the sacrificial gate is replaced with areplacement gate (such as the gate 2307 illustrated in FIGS. 33A, 33B,and 33C) as described above with reference to FIGS. 19A-23A, 19B-23B,and 19C-23C. In step 3815, the second spacer layer is removed to form anair gap (such as the gap 2401 illustrated in FIGS. 33A, 33B, and 33C)between the protection layer and the first spacer layer as describedabove with reference to FIGS. 24A, 24B, and 24C. In step 3817, contactplugs (such as the contact plugs 2601 and 2603 illustrated in FIGS. 33A,33B, and 33C) are formed as described above with reference to FIGS. 25A,26A, 25B, 26B, 25C, and 26C.

FIG. 39 is a flow diagram illustrating a method 3900 of forming asemiconductor device in accordance with some embodiments. The method3900 starts with step 3901, where a sacrificial gate (such as the gate703 illustrated in FIGS. 7A, 7B, and 7C) is formed over an active region(such as the fin 501 illustrated in FIGS. 7A, 7B, and 7C) as describedabove with reference to FIGS. 2A-7A, 6B, 7B, and 7C. In step 3903, afirst spacer layer (such as the dielectric layer 801 illustrated inFIGS. 8A, 8B, and 8C) is formed along sidewalls and a top surface of thesacrificial gate as described above with reference to FIGS. 8A, 8B, and8C. In step 3905, a first protection layer (such as the protection layer901 illustrated in FIGS. 34A, 34B, and 34C) is formed over the firstspacer layer as described above with reference to FIGS. 9A, 9B, and 9C.In step 3907, a second spacer layer (such as the dielectric layer 1101illustrated in FIGS. 11A, 11B, and 11C) is formed over the firstprotection layer as described above with reference to FIGS. 11A, 11B,and 11C. In step 3909, epitaxial source/drain regions (such as theepitaxial source/drain regions 1501 illustrated in FIGS. 34A, 34B, and34C) are formed in the active region as described above with referenceto FIGS. 12A-16A, 12B-16B, and 12C-16C. In step 3911, a secondprotection layer (such as the protection layer 3201 illustrated in FIGS.34A, 34B, and 34C) is formed over the second spacer layer and theepitaxial source/drain regions as described above with reference toFIGS. 32A, 32B, and 32C. In step 3913, a third spacer layer (such as thedielectric layer 1801 illustrated in FIGS. 34A, 34B, and 34C) is formedover the second protection layer as described above with reference toFIGS. 18A, 18B, and 18C. In step 3915, the sacrificial gate is replacedwith a replacement gate (such as the gate 2307 illustrated in FIGS. 34A,34B, and 34C) as described above with reference to FIGS. 19A-23A,19B-23B, and 19C-23C. In step 3917, the second spacer layer is removedto form an air gap (such as the gap 2401 illustrated in FIGS. 34A, 34B,and 34C) between the first protection layer and the second protectionlayer as described above with reference to FIGS. 24A, 24B, and 24C. Instep 3919, contact plugs (such as the contact plugs 2601 and 2603illustrated in FIGS. 34A, 34B, and 34C) are formed as described abovewith reference to FIGS. 25A, 26A, 25B, 26B, 25C, and 26C.

FIG. 40 is a flow diagram illustrating a method 4000 of forming asemiconductor device in accordance with some embodiments. The method4000 starts with step 4001, where a sacrificial gate (such as the gate703 illustrated in FIGS. 27A, 27B, and 27C) is formed over an activeregion (such as the fin 501 illustrated in FIGS. 27A, 27B, and 27C) asdescribed above with reference to FIGS. 2A-7A, 6B, 7B, and 7C. In step4003, a first spacer layer (such as the dielectric layer 801 illustratedin FIGS. 27A, 27B, and 27C) is formed along sidewalls and a top surfaceof the sacrificial gate as described above with reference to FIGS. 27A,27B, and 27C. In step 4005, a portion of the first spacer layer is dopedto form a first protection layer (such as the protection layer 2801illustrated in FIGS. 28A, 28B, and 28C) as described above withreference to FIGS. 28A, 28B, and 28C. In step 4007, a second spacerlayer (such as the dielectric layer 1101 illustrated in FIGS. 11A, 11B,and 11C) is formed over the first protection layer as described abovewith reference to FIGS. 11A, 11B, and 11C. In step 4009, epitaxialsource/drain regions (such as the epitaxial source/drain regions 1501illustrated in FIGS. 35A, 35B, and 35C) are formed in the active regionas described above with reference to FIGS. 12A-16A, 12B-16B, and12C-16C. In step 4011, a second protection layer (such as the protectionlayer 3201 illustrated in FIGS. 35A, 35B, and 35C) is formed over thesecond spacer layer and the epitaxial source/drain regions as describedabove with reference to FIGS. 32A, 32B, and 32C. In step 4013, a thirdspacer layer (such as the dielectric layer 1801 illustrated in FIGS.35A, 35B, and 35C) is formed over the second protection layer asdescribed above with reference to FIGS. 18A, 18B, and 18C. In step 4015,the sacrificial gate is replaced with a replacement gate (such as thegate 2307 illustrated in FIGS. 35A, 35B, and 35C) as described abovewith reference to FIGS. 19A-23A, 19B-23B, and 19C-23C. In step 4017, thesecond spacer layer is removed to form an air gap (such as the gap 2401illustrated in FIGS. 35A, 35B, and 35C) between the first protectionlayer and the second protection layer as described above with referenceto FIGS. 24A, 24B, and 24C. In step 4019, contact plugs (such as thecontact plugs 2601 and 2603 illustrated in FIGS. 35A, 35B, and 35C) areformed as described above with reference to FIGS. 25A, 26A, 25B, 26B,25C, and 26C.

In accordance with an embodiment, a method including: forming asacrificial gate structure over an active region; forming a first spacerlayer along sidewalls and a top surface of the sacrificial gatestructure; forming a first protection layer over the first spacer layer;forming a second spacer layer over the first protection layer; forming athird spacer layer over the second spacer layer; replacing thesacrificial gate structure with a replacement gate structure; andremoving the second spacer layer to form an air gap between the firstprotection layer and the third spacer layer. In an embodiment, themethod further includes forming a second protection layer between thesecond spacer layer and the third spacer layer. In an embodiment, thefirst protection layer and the second protection layer include a samematerial. In an embodiment, the first protection layer and the secondprotection layer include different materials. In an embodiment, formingthe first protection layer over the first spacer layer includesdepositing a carbon layer or a boron layer over the first spacer layer.In an embodiment, removing the second spacer layer includes performing aselective etch process on the second spacer layer. In an embodiment, themethod further includes, before forming the third spacer layer, formingan epitaxial source/drain region in the active region adjacent thesacrificial gate structure.

In accordance with another embodiment, a method including: forming asacrificial gate structure over an active region; depositing a firstspacer layer along sidewalls and a top surface of the sacrificial gatestructure; doping an upper portion of the first spacer layer to form afirst protection layer over an un-doped portion of the first spacerlayer; depositing a second spacer layer over the first protection layer;forming an epitaxial source/drain region in the active region adjacentthe sacrificial gate structure; depositing a third spacer layer over thesecond spacer layer and the epitaxial source/drain region; replacing thesacrificial gate structure with a replacement gate structure; andperforming a selective etch process on the second spacer layer to forman air gap between the first protection layer and the third spacerlayer. In an embodiment, the method further includes forming a secondprotection layer between the second spacer layer and the third spacerlayer. In an embodiment, forming the second protection layer includesdepositing a carbon layer or a boron layer. In an embodiment, doping theupper portion of the first spacer layer includes doping a material ofthe first spacer layer with carbon or boron. In an embodiment, an etchrate of the first protection layer is less than an etch rate of theun-doped portion of the first spacer layer with respect to the selectiveetch process. In an embodiment, doping the upper portion of the firstspacer layer includes performing a plasma-assisted doping process on thefirst spacer layer. In an embodiment, forming epitaxial source/drainregion includes: etching the first spacer layer, the second spacerlayer, the first protection layer and the active region to form arecess; and epitaxially growing a semiconductor material in the recess.

In accordance with yet another embodiment, a device including: a gatestructure over an active region; a first spacer extending along asidewall of the gate structure and a top surface of the active region; afirst protection layer adjacent the first spacer, the first spacer beinginterposed between the sidewall of the gate structure and the firstprotection layer; a second spacer adjacent the first protection layer,the first protection layer being interposed between the first spacer andthe second spacer; and an air gap interposed between the firstprotection layer and the second spacer. In an embodiment, the devicefurther includes a second protection layer between the first protectionlayer and the second spacer. In an embodiment, the air gap is interposedbetween the first protection layer and the second protection layer. Inan embodiment, the second protection layer is a carbon layer or a boronlayer. In an embodiment, the first protection layer is a carbon layer ora boron layer. In an embodiment, the first spacer is formed of a firstmaterial, and the first protection layer is formed of the first materialdoped with carbon or boron.

In accordance with yet another embodiment, a device includes: a gatestructure over an active region; an epitaxial source/drain regionextending into the active region adjacent the gate structure; and aspacer structure on a sidewall of the gate structure, the spacerstructure including: a first layer extending along the sidewall of thegate structure; a second layer adjacent the first layer, the secondlayer extending along and being in physical contact with a top surfaceof the epitaxial source/drain region; and an air gap interposed betweenthe first layer and the second layer, a first surface of the first layerand a second surface of the second layer being exposed by the air gap.

In accordance with yet another embodiment, a device includes: a gatestructure over an active region; an epitaxial source/drain regionextending into the active region adjacent the gate structure; and aspacer structure between the gate structure and the epitaxialsource/drain region, the spacer structure including: a first layerextending along a top surface of the active region and being in physicalcontact with a sidewall of the epitaxial source/drain region; a secondlayer adjacent the first layer, the second layer being in physicalcontact with the sidewall and a top surface of the epitaxialsource/drain region; and an air gap interposed between the first layerand the second layer, a first surface of the first layer, a secondsurface of the second layer, and a portion of the sidewall of theepitaxial source/drain region being exposed by the air gap.

In accordance with yet another embodiment, a method includes: forming asacrificial gate structure over an active region; forming a first spacerlayer along a sidewall of the sacrificial gate structure and a topsurface of the active region; forming a first protection layer over thefirst spacer layer; forming a second spacer layer over the firstprotection layer; forming an epitaxial source/drain region in the activeregion adjacent the sacrificial gate structure, a sidewall of theepitaxial source/drain region being in physical contact with the firstspacer layer, the first protection layer, and the second spacer layer;forming a third spacer layer over the second spacer layer and a topsurface of the epitaxial source/drain region; and etching the secondspacer layer to form an air gap between the first protection layer andthe third spacer layer.

The fins may be patterned by any suitable method. For example, the finsmay be patterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a gate structure over anactive region; an epitaxial source/drain region extending into theactive region adjacent the gate structure; and a spacer structure on asidewall of the gate structure, the spacer structure comprising: a firstlayer extending along the sidewall of the gate structure, wherein abottom surface of the first layer is below a top surface of theepitaxial source/drain region; a second layer adjacent the first layer,the second layer extending along and being in physical contact with thetop surface of the epitaxial source/drain region, wherein a bottomsurface of the second layer is below the top surface of the epitaxialsource/drain region; and an air gap interposed between the first layerand the second layer, wherein a first surface of the first layer and asecond surface of the second layer are exposed by the air gap.
 2. Thedevice of claim 1, wherein the first layer is a carbon layer or a boronlayer.
 3. The device of claim 1, wherein the second layer comprises adielectric material.
 4. The device of claim 1, wherein the air gapexposes a sidewall of the epitaxial source/drain region.
 5. The deviceof claim 1, wherein the first layer is in physical contact with asidewall of the epitaxial source/drain region.
 6. The device of claim 1,wherein the second layer is in physical contact with a sidewall of theepitaxial source/drain region.
 7. The device of claim 1, wherein thespacer structure further comprises a third layer interposed between thesidewall of the gate structure and the first layer, the third layerbeing in physical contact with a sidewall of the epitaxial source/drainregion.
 8. A device comprising: a gate structure over an active region;an epitaxial source/drain region extending into the active regionadjacent the gate structure; and a spacer structure between the gatestructure and the epitaxial source/drain region, the spacer structurecomprising: a first layer extending along a top surface of the activeregion and being in physical contact with a sidewall of the epitaxialsource/drain region; a second layer adjacent the first layer, the secondlayer being in physical contact with the sidewall and a top surface ofthe epitaxial source/drain region; and an air gap interposed between thefirst layer and the second layer, a first surface of the first layer, asecond surface of the second layer, and a portion of the sidewall of theepitaxial source/drain region being exposed by the air gap.
 9. Thedevice of claim 8, further comprising a dielectric layer over the gatestructure, wherein a portion of the dielectric layer extends into theair gap.
 10. The device of claim 8, wherein the first layer and thesecond layer comprise different materials.
 11. The device of claim 8,wherein the first layer comprises a boron-doped layer or a carbon-dopedlayer.
 12. The device of claim 8, further comprising a contact plugextending through the second layer and electrically coupled to theepitaxial source/drain region.
 13. The device of claim 8, wherein thespacer structure further comprises a third layer interposed between asidewall of the gate structure and the first layer, the third layerbeing made of a first material.
 14. The device of claim 13, wherein thesecond layer is made of the first material doped with carbon or boron.15. A method comprising: forming a sacrificial gate structure over anactive region; forming a first spacer layer along a sidewall of thesacrificial gate structure and a top surface of the active region;forming a first protection layer over the first spacer layer; forming asecond spacer layer over the first protection layer; forming anepitaxial source/drain region in the active region adjacent thesacrificial gate structure, a sidewall of the epitaxial source/drainregion being in physical contact with the first spacer layer, the firstprotection layer, and the second spacer layer; forming a third spacerlayer over the second spacer layer and a top surface of the epitaxialsource/drain region; and etching the second spacer layer to form an airgap between the first protection layer and the third spacer layer. 16.The method of claim 15, wherein forming the first protection layer overthe first spacer layer comprises depositing a carbon layer or a boronlayer over the first spacer layer.
 17. The method of claim 15, whereinforming the first protection layer over the first spacer layer comprisesdoping an upper portion of the first spacer layer with carbon or boron.18. The method of claim 17, wherein doping the upper portion of thefirst spacer layer comprises performing a plasma-assisted doping processon the first spacer layer.
 19. The method of claim 15, furthercomprising, before etching the second spacer layer, replacing thesacrificial gate structure with a replacement gate structure.
 20. Themethod of claim 19, further comprising depositing a dielectric layerover the replacement gate structure, wherein a portion of the dielectriclayer extends into the air gap.